Galectin-9 (Gal-9) is a member of the galectin family, and exhibits physiological activity upon binding to β galactoside of N- or O-glycan (Non-Patent Document 1). Galectin-9 was first discovered and identified as a T cell apoptosis-inducing factor (Non-Patent Document 2) and an eosinophil chemotactic factor (Non-Patent Document 3). From then on, a wide variety of activities of galectin-9 have been reported up to the present. Galectin-9 acts on T cells in the following manner: galectin-9 binds to Tim-3 to induce apoptosis of Tim-3 positive TH1 cells, thereby settling down excess TH1 reactions to inhibit autoimmune inflammation (Non-Patent Document 4). A TH17 cell is considered to be a cause or one of exacerbating factors of various intractable diseases such as autoimmune diseases, allergies, and cancers, and this cell also expresses Tim-3 (Non-Patent Documents 5 to 6). Administration of galectin-9 decreases TH17 cells, and increases inflammation inhibitory Treg cells (Non-Patent Document 7). At present, involvement of Tim-3 in this decrease in TH17 cells and the mechanism by which such decrease occurs are unknown.
As actions of galectin-9 on cells other than T cells, the following actions are known in addition to the above-described eosinophilotactic activity: induction of CD11bLy-6C monocytic myeloid-derived suppressor cells (Non-Patent Document 8); induction of CD11bLy-6G neutrophilic myeloid-derived suppressor cells (Non-Patent Documents 9 to 10); induction of plasmacytoid dendritic cells (Non-Patent Document 11); and inhibition of degranulation from mast cells (Non-Patent Document 12). Many of previous reports focus on the action of galectin-9 for inhibiting exaggerated immunoreactions. However, in some situations, galectin-9 enhances immunity. Galectin-9 binds to Tim-3 on monocytes and dendritic cells to activate these cells, thereby promoting the production of inflammatory cytokines (Non-Patent Document 13). Also, when galectin-9 interacts with Tim-3 in macrophages, immunity for eliminating tubercle bacilli is enhanced (Non-Patent Document 14). That is to say, galectin-9 can modulate immunity bidirectionally.